Are Radial Tractor Tires Cost Effective?

James C. Frisby
Department of Agricultural Engineering, University of Missouri-Columbia
When Pirelli Co. developed the first radial tractor tire in 1957, the company claimed it would develop 20 percent greater traction with less slippage at equal load than an equivalent bias-ply tire. (Forrest, et al. 1962) Subsequent research has confirmed that radial tires have the advantage in tractive efficiency. H. Erdal Ozkan, state extension specialist at Ohio State University, has reviewed all available research results related to field performance of tractors equipped with radial and bias ply tires.

Author

Increase in tractive efficiency for radials

Seleznev and Kovalez (1968)

13 percent

Bohnert and Kenady (1975)

7 percent

Hoffman (1983)

8 to 9.5 percent

Hausz and Akins (1980)

7 to 13 percent

In most cases, the research was done with the same wheel slip for radial and bias tires. This may have kept the radial tires from reaching the predicted 20 percent advantage.

Drawbar pull tests were reported as follows:

Author

Wheel slip

Soil

Advantage of radial

Forrest (1962)

less than 15 percent

SandLoamClay

8 percent23 percent21 percent

Thaden (1962)

16 percent



29 percent

Mumgaard and Rudakov (1975)

15 percent

Firm

15.5 percent

Bohnert and Kenady (1975)



TilledSod

14.6 percent18.8 percent

Gee-Clough (1977)

20 percent



5-8 percent

Field capacity and fuel consumption were studied:

Author

Increase in field capacity for radials

Reduction in fuel consumption for radials

Seleznev and Kovalez (1986)

10.7 percent

13 percent

B.F. Goodrich Co. (1981)

12.3 percent

12.8 percent

Bohnert and Kenady (1975)



16.4 percent

Hauck and Kucera (1983)

2.1 percent

6.5 to 8.1 percent

Hausz and Akins (1980)

5 to 7 percent

6 to 10 percent

Conditions used by investigators were not constant, and results cannot be directly compared. Radial tires, however, do seem to have the advantage in every category except purchase price. Resistance to abrasive wear seems about the same for radial and bias tires, but radial tires have much longer tread life than bias tires. Radial tires will have service life 25 to 40 percent longer than equivalent bias tires (Ozkan, 1986).

Ownership cost usually includes depreciation, interest on investment, tax, shelter and insurance. For a comparison of tires, the difference in tax, shelter and insurance cost was thought to be negligible and was omitted. The capital recovery factor was used to estimate ownership cost because it accounts for both depreciation and return on investment.

To compute annual tire ownership cost; unit tire cost; fuel cost for radial and bias tires; labor cost for radial and bias tires; and total savings per hour and hours use required to break even, use the following equations: